Elastomeric attenuators have been used for some time for joining wall panels to supporting frames that are subject to vibratory loads in an effort to reduce the amount of noise producing vibrations that are transmitted to the panel. One such application involves the mounting of the interior wall panels of an aircraft to the superstructure of the aircraft. There is an increased demand for reduced cabin noise levels and reduced aircraft weight. Accordingly, there is now a need for more compliant attenuator units that can replace those presently in use, but without having to increase the size and weight of these units.
Cylindrical elastomeric shock isolators have also been used for some time in the automobile industry to reduce the effect of road-induced load upon a vehicle's suspension system. Typically, these devices involve an inner tubular sleeve and an outer tubular sleeve with the sleeves being superimposed one over the other along a common longitudinal axis. An elastomeric bushing is mounted in the space between the two sleeves and the bushing in most cases is bonded to one or both sleeves. As explained in greater detail in U.S. Pat. No. 6,446,993, this type of bushing is generally mounted between the suspension system of the vehicle and its frame with the outer sleeve press fitted in the suspension system and the inner sleeve being secured to the frame by some type of fastener. A pair of opposed voids are sometimes placed longitudinally in the bushing to soften the spring rate of the bushing along the reaction axis of the system along which road induced forces are transmitted back into the suspension system. Forces that are transmitted into the bushing due to steering inputs act perpendicular to the reaction axis and are attenuated in the unvoided areas of the bushing, which have an increased spring rate thus providing the driver with a better feel of the road.
Although the above-described voided elastomeric isolators, as used in the automotive industry perform quite well to reduce the effect of road induced forces, these devices do not perform as well when dealing with vibratory induced noise and, in particular, noise in the mid and high range frequencies.